1. Field of the Invention
This invention relates to a process for producing a coke. More specifically, this invention relates to a process for producing a coke wherein filling density of a starting coal is increased, thereby making it possible to stabilize and improve qualities of the coke.
2. Description of the Prior Art
Cokes used in metallurgy are ordinarily produced by a method which comprises pulverizing one starting coal or a blend of two or more starting coals, charging the pulverizate into a coke oven and conducting carbonization. On this occasion, when filling density of the starting coal(s) within the coke oven is higher, the amount of heat in carbonization can be rendered smaller, and qualities of the resulting cokes are improved. That is, when the same starting coals are used and filled in high density, the cokes of higher qualities can be obtained, and less costly starting coals are usable to afford the cokes of equal qualities.
As a means of filling the starting coal in high density, there is commonly employed a method using a mixture of 10 to 30% by weight of a briquette having previously increased density and 90 to 70% by weight of a slack. This method however requires an equipment for producing the briquette and is therefore economically disadvantageous. Besides, as the uneven distribution of the briquette takes place in charging the starting coal into the coke oven, nonuniformity of qualities of the resulting coke occurs. Adhesion between coal particles provided by the moisture in the slack is indicated as one reason for the uneven distribution of the briquette.
The moisture in the slack is attributed to immersion of rainwater occurring when the starting coals are stacked outdoors or water sprinkling to prevent scattering of a coal dust, and the moisture content is usually 7 to 15% based on the weight of the starting coal.
As a method for preventing segregation of the briquette, there is proposed a method in which various surface active agents are added to the slack mixed with the briquette (Japanese Laid-open Patent Application Nos. 49693/1982 and 57861/1986).
However, it cannot necessarily be said that these methods can provide enough effects. A method is also known wherein the moisture content in the starting coal is reduced by heating the starting coal. This method gives a fixed effect in the aspect of improvement in filling density. Nevertheless, said method not only needs a device and steps for said effect but also seems likely to allow explosion of the dust of the starting coal within the device. For this reason, it cannot be employed.
As another method for increasing filling density of the starting coal, there are proposed methods in which various surface active agents (Japanese Laid-open Patent Application Nos. 21434/1980, 100892/1981 and 68691/1988), or mixtures of oils and surface active agents (Japanese Laid-open Patent Application Nos. 114801/1978 and 283685/1986) are added to the starting slack. However, in these methods, the oils have to be added in large amounts, and the effect becomes maximal with fixed amounts of the surface active agents. Thus, the effect is not altogether enough.
It is an object of this invention to provide a process for producing a high-quality coke which enables filling of a starting coal in high density.
The present inventors have made extensive studies to achieve the object and consequently found that if a starting coal is mixed with a high-molecular organic compound forming a hydrous gel, filling density of the starting coal is improved. This finding has led to completion of this invention.
By the way, it is disclosed in a great many prior arts as will be described below that varying compounds are added to a starting coal in preparing a briquette for production of a coke.
Japanese Laid-open Patent Application No. 18702/1976 discloses a process for producing a pelletized coke for preparation of iron which comprises adding to a slack a water-soluble organic binder selected from compounds having a hydrophilic group such as a hydroxyl group, a sulfonic acid group, an amino group or a carboxyl group and a hydrophobic group such as an aromatic group or a higher aliphatic group (examples thereof are lignin sulfonate, cellulose xanthate, tar sulfonate, alcohol fermentation residues of starches, etc.) as an aqueous solution having a concentration of 10 to 20%, pulverizing the mixture, drying the pulverizate and firing the dried product. Since the resulting pellets are however low in strength owing to the moisture, they cannot be charged as such in a carbonization oven for producing the pelletized coke and a drying step is required.
Japanese Laid-open Patent Application No. 82901/1977 describes that a methyl cellulose is added to a coarse powdery inferior coal. However, this prior art indicates a process in which a coal for producing a coke is prepared by blending a mixture of the inferior coal and a petroleum-type or coal-type bituminous material with a large amount (20 to 80% based on the mixture) of the methyl cellulose to form the inferior coal into an agglomerated powder, and blending it with another coal for coke.
Japanese Laid-open Patent Application No. 27332/1980 discloses binders for preparing briquettes to produce cokes for blast furnace, said binders containing molasses, blackstrap molasses or mixtures of them and surface active agents. This prior art indicates binders for preparing briquettes to produce cokes, the amounts of the binders being preferably 1 to 10% by weight based on the coals.
Japanese Laid-open Patent Application No. 142982/1983 describes a process for producing briquettes charged into a coke oven. The process of this prior art forms a coating on the surface of the briquette at normal temperatures, which coating disappears by thermal decomposition, combustion or evaporation when heated in a coke oven chamber. As a material for forming the coating, high-molecular materials such as polyvinyl acetate, polyvinyl alcohol, polyolefins, polyesters and polyvinyl chloride are available.
Japanese Laid-open Patent Application No. 44583/1985 discloses a process in which a starting coal is blended with a bituminous material and a water-soluble thermosetting material (e.g. starches, pulp waste liquors, molasses and polyvinyl alcohol), and the blend is kneaded and pressure-molded to obtain briquettes for production of cokes.
Japanese Laid-open Patent Application No. 212493/1987 involves a method for determining an amount of a binder for pseudo-powdering a slack to prevent formation of a dust in case of pseudo-powdering the slack to produce a dry coal or a preheated coal. An aqueous solution of dextrin or polyvinyl alcohol is shown as the binder.
The foregoing prior arts are concerned with briquettes used to produce cokes or preparation of the briquettes. They do not aim at improvement in the filling density of the starting coal when obtaining the coke directly from the coal and improvement in qualities of the coke thereby brought forth, nor do they indicate the additives used in this invention.
Additives are added to the coal for the other various purposes than as mentioned above. For instance, U.S. Pat. No. 4,055,471, GB No. 1,496,303, GB No. 1,496,302, NL No. 7,515,201 and DE No. 2,500,606 describe that in order to decrease entraining of a dust in charging a hot coal into a coke oven, aqueous solutions of adhesives such as a sulfide salt waste liquor, a starch, dextrin, molasses, casein and a glue are added, if required, with a coarse coal tar and a wetting agent. According to this method, coal fine particles are agglomerated by the action of the above adhesive aqueous solutions, etc., to prevent entraining of the coal dust. The adhesive is added as an aqueous solution having a concentration of 30 to 70%. Said method differs from this invention in additives and purpose thereof.
It is not said that mixing the coal with a hydrous gel used in this invention or its similar compounds has not been so far conducted at all.
For example, Japanese Laid-open Patent Application No. 60784/1986 contemplates a method for reducing the moisture content of products piled outdoors characterized in that when loading or delivering raw materials (coals, etc.) stacked outdoors, a water-absorbing molded article made of a water-absorbing resin is localized in and/or on the raw materials to absorb to said water-absorbing molded article the moisture or rainwater adhered to the raw materials, and the water-absorbing molded article is then separated from the raw materials.
Japanese Laid-open Patent Application No. 111209/1986 discloses that in order to prevent immersion of rainwater into carbonaceous materials stacked outdoors, a water-absorbing polymer is scattered on the carbonaceous materials to form coatings on their surfaces.
Japanese Laid-open Patent Application No. 151294/1986 discloses that in order to save energy by reducing a moisture in a coal, said coal is mixed with a water-absorbable and -desorbable resin to adsorb the moisture in the coal to the resin, then separating the coal from the resin, removing water from the recovered resin, and reusing said resin to remove the moisture in the coal.
The methods disclosed in the above literature are however different from this invention in the purpose and period of adding the additives to the coal, the position of storing (using) the coal to which the additives are added, or the use method of the additives.